2.6.1 Surface water numerical modelling for the Galilee subregion

Executive summary

Artesian Spring Wetland at  Doongmabulla Nature Refuge, QLD, 2013 Credit: Jeremy Drimer, University of Queensland

Coal and coal seam gas (CSG) development can potentially affect water-dependent assets (either negatively or positively) through a direct impact on surface water hydrology. This product provides modelled estimates of potential surface water changes due to likely coal resource development in the Galilee subregion. The methods are summarised, followed by details regarding the development of the model. The product concludes with predictions of the hydrological response variables, the hydrological characteristics of the system that potentially changes due to coal resource development (for example, drawdown or the annual flow volume). The uncertainty and limitations of the models are also reported.

Results are reported for the two potential futures considered in a bioregional assessment (BA):

  • baseline coal resource development (baseline): a future that includes all coal mines and CSG fields that are commercially producing as of December 2012 (if any)
  • coal resource development pathway (CRDP): a future that includes all coal mines and CSG fields that are in the baseline as well as those that are expected to begin commercial production after December 2012.

The difference in results between baseline and the CRDP is the change that is primarily reported in a BA. This change is due to the additional coal resource development – all coal mines and CSG fields, including expansions of baseline operations that are expected to begin commercial production after December 2012.

There are no coal or CSG developments in operation as of the last quarter of 2012 for the Galilee subregion for the baseline. There are 17 proposed new developments in the Galilee subregion for the CRDP. There is enough information available to include seven of these developments in the numerical modelling for the Galilee subregion.

The seven development projects being modelled are the open-cut coal mines Alpha Coal Project and Hyde Park Coal Project, and the combined open-cut and underground coal mines Carmichael Coal Mine Project, China First Coal Project, China Stone Coal Project, Kevin’s Corner Coal Project and South Galilee Coal Project.

A generic methodology for surface water numerical modelling in BA is presented in companion submethodology M06 (as listed in Table 1). This product describes how the methodology has been applied in the Galilee subregion. Numerical simulation of the likely changes in surface water due to coal resource development requires a model or model sequence that can simulate change in the: regional groundwater system, the alluvial groundwater system, and the stream network. In the BA for the Galilee subregion an indirectly coupled model sequence of two models – consisting of a regional groundwater analytical element model (referred to as GW AEM) and a rainfall-runoff model (the Australia Water Resources Assessment landscape model, referred to as AWRA-L) – is used to simulate the hydrological changes on the surface water systems of the subregion. Development of a single coupled and integrated surface water and groundwater model is beyond the resources and data available for this assessment of the Galilee subregion.

The surface water modelling domain comprises the Belyando, Cape and Suttor river basins and includes 61 model nodes at which daily streamflow is predicted. The model simulation period is from 2013 to 2102.

The comparison among the 61 model nodes shows that for the hydrological response variables that characterise high-streamflow conditions, the relative hydrological changes are largest for the model nodes where the maximum additional coal resource development percentage is largest. In general, the biggest changes (flow reductions of up to 20%) occur immediately downstream of additional coal resource development and are particularly evident in model nodes where the mine footprint forms a large proportion of the node catchment. For every high-streamflow hydrological response variable, the biggest changes are predicted to occur at a model node with a small upstream catchment on Sandy Creek. This node is located downstream of the South Galilee Coal Project.

The changes due to additional coal resource development on the low-streamflow hydrological response variables are more substantial than those on the high-streamflow hydrological response variables. However, they are also associated with greater uncertainty in both the predicted change and the year of maximum change. For the low-streamflow variables the biggest impacts occur in the middle reaches of the Belyando River and reflect an accumulation of impacts from multiple developments. These results also indicate that changes to low-streamflow characteristics are caused by a combination of the instantaneous impact of interception from the mine footprints of the additional coal resource development and the cumulative impact on baseflow over time caused by drawdown of the watertable, while the changes to high-streamflow characteristics are dominated by direct interception of runoff.

The change in baseflow due to changes in surface water – groundwater interactions under the CRDP is small compared to other components of the water balance and the effect of rainfall interception by mine sites. In the Galilee subregion, the accuracy with which mine footprints are represented depends fully on the resolution of the planned mine footprints provided by the mine proponents. This, therefore, is one of the crucial aspects of the surface water model as it potentially has a high impact on predictions and it is driven by data availability rather than availability of resources or technical issues.

Outputs from the surface water modelling are used for product 2.7 (receptor impact modelling) and in product 3-4 (impact and risk analysis) for the Galilee subregion.

Last updated:
6 December 2018
Thumbnail of the Galilee subregion